FPS games tend to stick to fairly standard formulas; all out brawls (such as team deathmatch, capture-the-flag, etc) with unlimited re-spawns, or the more personal, one life/one death matches (think Search and Destroy from COD, or Execution/Warzone in Gears).
R2 seems to try to combine these two; small squads that have their own objectives as part of a much larger team. L4D combines these in another way...as part of the four, you have one life and have to survive the zombie attack. You work together as a team to defeat a horde of zombies. As a zombie, you have multiple re-spawns and your only goal is to kill the four.
The best of both worlds, mashed together by Valve. I am excited as hell for this game. Given Valves recent warming-up to the PS3, I'd be surprised if PS3 owners don't get their own version eventually. More time to get hyped for it I guess?